Cylinder type air damper

ABSTRACT

A cylinder type air damper includes a cylinder having at least one rib projecting radially inwardly and extending in the axial direction, a piston inserted for reciprocation within the cylinder and axially dividing the interior of the cylinder into a front compartment and a rear compartment. An exhaust hole axially penetrates the piston and is provided with a valve for blocking the exchange of air between the two compartments in response to an axial movement of the piston in one direction. An orifice also axially penetrates the piston within an area thereof subject to blocking by means of the valve for permitting the exchange of air between the two compartments in response to the axial movement of the piston. A vent duct communicates at one end with the orifice and is open at the other end within an area other than the area subject to blocking by means of the valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cylinder type air damper and, moreparticularly, to an air damper for providing a braking force which isvariable according to the load applied thereto.

2. Description of the Prior Art

Air dampers of this type generally comprise a cylinder, a pistoninserted for reciprocation within the cylinder and axially dividing theinterior of the cylinder into front and rear compartments, an orificeaxially penetrating the piston for permitting the exchange of airbetween the two compartments in response to axial movement of thepiston, and an exhaust hole axially penetrating the piston and providedwith a valve for preventing the exchange of air between the twocompartments in response to the axial movement of the piston in onedirection, as disclosed in Japanese Utility Model Publication SHO62-24845, Japanese Utility Model Public Disclosure SHO 63-190946, U.S.Pat. No. 4,796,732 and U.S. Pat. No. 4,856,625.

However, the above prior art air dampers have a problem in that thespeed of the piston varies with a change in the load exerted upon theair damper.

Since the orifice diameter is fixed, the piston speed is increased withan increasing load impressed upon the damper. For instance, when thisdamper is used in connection with a door pivoted downwardly about ashaft disposed at the lower end of the door when it is opened, such as,for example, the door of an automobile glove compartment or the like,such that its braking force is utilized when the door is pivoteddownwardly, the load exerted upon the damper increases as the door ispivoted downwardly. Therefore, the door opening speed is initially lowand accelerates as the door approaches the end of the opening movement.

OBJECT OF THE INVENTION

One object of the invention is to provide an air damper in which thepiston can be moved substantially at a constant speed irrespective ofthe load impressed upon the damper. In other words, one object of theinvention is to provide an air damper which is capable of varying thebraking force in a direction tending to cancel or compensate for anyload variation.

SUMMARY OF THE INVENTION

To attain the above object of the invention, there is provided acylinder type air damper which comprises a cylinder, a piston insertedfor reciprocation within the cylinder and axially dividing the interiorof the cylinder into a front compartment and a rear compartment, anorifice axially penetrating the piston so as to permit an exchange ofair between the two compartments in response to an axial movement of thepiston, and an exhaust hole axially penetrating the piston and providedwith a valve for blocking the exchange of air between the twocompartments in response to the axial movement of the piston in onedirection, and wherein the orifice is open within a region subject toblockage by means of the valve, and wherein further, a vent duct isprovided between the orifice and the valve such that it communicates atone end with the orifice and opens at the other end within a regionother than the region subject to blockage by means of the valve, or inwhich the inner periphery of the cylinder is provided with at least onerib projecting radially inwardly and extending in the axial direction ofthe piston.

With the air damper having a vent duct, when the speed of the pistontends to increase with increasing load impressed thereon, the valve isforcibly seated and deformed so as to reduce the opening area of thevent duct, thus throttling the air entering the orifice from the ventduct and increasing the braking force. For this reason, the brakingforce can be varied in a direction tending to cancel or compensate forthe load variation. It is thus possible to maintain a substantiallyconstant piston speed.

With the air damper having at least one rib provided upon the innerperiphery of the cylinder, a gap is provided between the inner peripheryof the cylinder and the outer periphery of the piston at the position ofthe rib, and this gap constitutes a bypass enabling exchange of airbetween the two compartments defined by the piston, thus reducing thebraking force. It is thus possible, by means of providing the rib withinan area of the damper at which the initial piston speed characteristicof the load is small, to increase the piston speed within such areawithin which the initial piston speed is exhibited. Furthermore, due tothe absence of the rib within the final piston speed area where the loadbecomes large, the braking force is increased. For this reason, it ispossible to suppress the tendency for the piston speed to increase withincreasing load.

Thus, like the air damper having the vent duct, the braking force can bevaried in a direction tending to cancel or compensate for the loadvariation, and thus it is possible to maintain a substantially constantpiston speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will becomemore apparent from the following detailed description with reference tothe accompanying drawings, in which like reference characters designatelike or corresponding parts throughout the several views, and wherein:

FIG. 1 is an exploded perspective view showing an embodiment of the airdamper according to the invention;

FIG. 2 is a perspective view, partly broken away, showing the cylinderof the air damper shown in FIG. 1;

FIG. 3 is a sectional view taken along 3--3 in FIG. 2;

FIG. 4 is a plan view, partly in section, showing the cap of the airdamper shown in FIG. 1;

FIG. 5 is a side view showing the cap shown in FIG. 4;

FIG. 6 is a side view showing the piston of the air damper shown in FIG.1;

FIG. 7 is a sectional view taken along line 7--7 in FIG. 6;

FIG. 8 is a sectional view taken along line 8--8 in FIG. 6;

FIG. 9 is a sectional view showing the valve of the air damper shown inFIG. 1;

FIG. 10 is a plan view, partly broken away, showing a rod of the airdamper shown in FIG. 1;

FIG. 11 is the front view showing the rod of FIG. 10;

FIG. 12 is a plan view, partly broken away, showing the piston and rodjoined together;

FIG. 13 is a plan view, partly broken away, showing the air damper shownin FIG. 1 in its assembled state;

FIG. 14 is a side view showing the air damper shown in FIG. 1;

FIG. 15 is a plan view, partly broken away, showing the air damper shownin FIG. 1, with the view being along a line of sight perpendicular tothat of FIG. 13;

FIG. 16(a) is a sectional view showing the valve of FIG. 9 in aninoperative state;

FIG. 16(b) is a sectional view showing the valve of FIG. 9 in anoperative state; and

FIG. 17 is an explanatory view showing the air damper of FIG. 1 in useupon a downwardly opening closure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawings illustrate an embodiment of the cylinder type air damperconstructed according to the present invention. In the Figures,reference numeral 1 designates a cylinder type air damper. The airdamper 1, as shown in FIG. 1, comprises a cylinder 2 open at one end, acap 3 closing the open end of the cylinder 2, a piston 4 inserted forreciprocation within the cylinder 2 and axially dividing the interior ofthe cylinder 2 into front and rear compartments 2a and 2b, and a pistonrod 5 extending axially from the piston 4 and penetrating the cap 3 soas to project outside thereof. The individual components are plasticmoldings.

As shown in FIGS. 2 and 3, the cylinder 2 has at least one integral rib6 projecting radially inwardly and extending in the axial direction ofthe piston 4. It is molded from, for example, polyoxymethylene and hasadequate rigidity and elasticity. In this embodiment, the ribs 6 extendfrom the inner surface of the blind end wall of the cylinder 2 towardthe open end thereof. They extend along the inner periphery of thecylinder 2 for a distance approximately equal to one third of the lengthof the cylinder. They are parallel and comparatively close to oneanother. This arrangement of ribs, however, is by no means limitative.

As shown in FIGS. 1, 4 and 5, the cap 3 is cylindrical and is closed atone end. Its end wall has a central circular through hole 7 penetratedby means of the rod 5 and a pair of notches 8 extend diametricallyoppositely outwardly from the through hole 7. Similar to the cylinder 2,the cap 3 is made of polyoxymethylene.

The cap 3 and cylinder 2 are provided with respective locking means forengagement with each other. In the illustrated embodiment, the cylinder2 has its outer periphery near its open end provided with a pluralityof, that is, four, integral projections 9 each having a sawtoothedsectional profile with a rearward inclined surface 9', whereas the cap 3has four engagement holes 10 formed at positions corresponding to therespective projections 9 for receiving the same.

The projections 9 and engagement holes 10 are provided at non-uniformintervals in the circumferential direction, thus providing fordirectivity at the time of assembly. The inner periphery of the cap 3 isformed with guide grooves 11 extending axially inward from its open endand tapering toward the respective engagement holes 10. The cylinder 2and cap 3 have equal outer diameters, and the outer diameter of theportion of the cylinder 2 adjacent to the open end thereof is madeslightly less than or substantially equal to the inner diameter of thecap 3, thus preventing formation of a step between the two components asseen in FIGS. 13 and 15.

Between the cap 3 and the cylinder 2, a filter sheet 12 is interposedand fitted within the cap 3 as shown in FIG. 1. This filter sheet 12serves to filter out dust that may be in the air that is introducedthrough the gap defined between the cap 3 and the rod 5. It is made fromfoamed sponge, for example. The filter sheet 12 has a central slot 13which is penetrated by means of the rod 5. In order to retain the filtersheet 12 upon the inner side of the cap 3, the cap 3 has the innersurface of its end wall formed with a pair of holding portions 14extending upon the opposite sides of the through hole 7 and disposedwithin a plane which is perpendicular to that of the notches 8 of thecap 3. The holding portions 14 are fitted within the slot 13 of thefilter sheet 12 by slightly increasing the length of the slot 13 bymaking use of the elasticity of the filter sheet 12, thus securing thefilter sheet 12 in the cap 3 (FIGS. 13 and 15).

As shown in FIGS. 6 to 8, the piston 4 is cylindrical and is closed atone end. It is molded from, for example, nylon having adequate rigidityand elasticity. The piston 4 has its outer periphery formed with aring-like groove 16 in which an O-ring 15 is disposed. The piston 4 hasits radial wall 4' formed with an orifice 17 which axially penetratesthe wall 4' and permits exchange of air between the two compartments 2aand 2b in response to axial movement of the piston 4, and also withexhaust holes 19 which also axially penetrate the wall 4' and serve toblock the exchange of air between the two compartments 2a and 2b inresponse to axial movement of the piston in one direction. The O-ring 15is made of silicone rubber (FIG. 1).

As shown in FIG. 9, a valve 18 is umbrella-shaped and has a contactportion 20 and a shaft-like portion 21 extending from the center of thecontact portion 20 and is formed in a longitudinally intermediateportion with an annularly projecting retaining portion 21'. It is moldedfrom silicon rubber, the hardness of which is higher than that of theO-ring 15, such as, for example, approximately 50. The radial wall 4' ofthe piston 4 has a comparatively large hole 22 slightly eccentric withrespect to its center. The shaft-like portion 21 of the valve 18 isinserted through the hole 22.

As shown in FIG. 6, the orifice 17 and exhaust holes 19 are arrangedalong a circle concentric with the hole 22. In this embodiment, eightholes are formed such that they inscribe a circle concentric with thehole 22 and within the largest diameter of the contact portion 20 of thevalve 18 and each has a diameter of approximately 1 mm. One of theseholes constitutes the orifice 17, and the remaining holes constitute theexhaust holes 19. The hole serving as the orifice 17 communicates with avent groove 23 formed within the wall 4' of the piston 4 upon the sideof the wall in contact with the contact portion 20 of the valve 18. Thevent groove 23 has one end communicating with the orifice 17 and extendsbeyond the contact portion 20 of the valve 18. It has a depth ofapproximately 0.1 mm. The orifice 17 and exhaust holes 19 have adiameter of approximately 1 mm, and similar to the hole 22 they areformed by means of core pins (not shown) at the time of the molding.

As shown in FIGS. 10 and 11, the rod 5 has a flat elongate portion 24integral with a circular portion 25. Circumferentially spaced-apart legportions 26 extending integrally forwardly and obliquely from the frontsurface of the circular portion 25 integrally support a cylindricalportion 27 such that it is spaced apart from the front surface ofportion 25 as noted above. The rod 5, similar to the piston 4, is moldedfrom nylon. A ring-like sound-proof packing 28 is disposed upon stemportions of the leg portions 26 (FIG. 1). The packing 28 is made ofsponge high in elasticity, and its outer diameter is slightly greaterthan the inner diameter of the cylinder 2.

The piston 4 and rod 5 are provided with coupling means such that theymay be coupled to each other. In this embodiment, the piston 4, as shownin FIGS. 1 and 6 to 9, has a pair of T-shaped engaging portions 29 and apair of straight and wide guide portions 30. These portions 29 and 30extend integrally and rearwardly from the radial wall 4'. They arearranged such that they exchange alternately along the outer peripheryof the cylindrical portion 27 of the rod 5. The two engaging portions29, as well as the two guide portions 30, diametrically oppose eachother. The inner surface of each guide portion 30 is provided with anintegral ridge 31 extending in the axial direction of the piston 4. Onthe other hand as shown in FIGS. 1, 10 and 11, the rod 5 has the outerperiphery of its cylindrical portion 27 provided with a pair of integralpawls 32 for engaging the inner side of extensions 29' extending fromthe opposite sides of the free end portion of each of the engagingportions 29 and is also provided with guide grooves 33 for receiving theridges 31 of the guide portions 30. Each pawl 32 has a sawtoothedsectional profile and has a front inclined surface 32'.

The procedure for assembling the air damper 1 will now be described

First, as shown in FIG. 12, O-ring 15 is mounted as a result of itselasticity within the ring-like groove 16 of the piston 4. Theshaft-like portion 21 of the valve 18 is inserted rearwardly through thehole 22 of the piston 4, and it is retained within the hole 22 bypulling its retaining portion 21' through the hole 22 as a result of oras permitted by the elasticity of the retaining portion 21' (FIGS. 16(a)and 12).

Meanwhile, as shown in FIG. 12, the sound-proof packing 28 is mounted,as a result of its elasticity, upon the stem portions of the legportions 26. Since the leg portions 26 extend forwardly and obliquely,and are circumferentially spaced with respect to one another, thesound-proof packing 28 is urged against the front surface of thecircular portion 25 of the rod 5.

The piston 4 and rod 5 are coupled to each other by coupling theengaging portions 29 and guide portions 30 of the piston 4 with thepawls 32 and guide grooves 33 provided upon the outer periphery of thecylindrical portion 27 of the rod 5. At this time, the ridges 31 uponthe inner surfaces of the guide portions 30 are disposed within theguide grooves 33 formed within the outer periphery of the cylindricalportion 27. When the two components are fitted together, the ends of theengaging portions 29 engage with the pawls 32 upon the outer peripheryof the cylindrical portion 27. When the two components are stronglycoupled together at this time, the engaging portions 29 are urgedradially outwardly by means of the inclined surfaces 32' of the pawls 32so as to ride upon and clear the pawls 32, whereupon they are restoredby means of their elastic restoring forces so as to obtain engagement ofthe perpendicular rear surfaces of the pawls 32 with the inner surfacesof the extensions 29' of the engaging portions 29. Thus, the engagingportions 29 are retained against withdrawal, and the piston 4 and rod 5are thus coupled to each other (FIG. 12).

When the piston 4 and the rod 5 are thus coupled together, the flatelongate portion 24 of the rod 5 is inserted from the rear end thereofthrough the slot 13 of the filter sheet 12, and then the cap 3 is fittedfrom its open end such that the rod 5 penetrates the hole 7 and notches8 defined upon the opposite sides of the hole 7. The filter sheet 12 isthen moved along the flat elongate portion 24 of the rod 5 so as to beheld by means of the holding portions 14 upon the inner surface of theend wall of the cap 3. At this time, the slot 13 of the filter sheet 12and notches 8 of the cap 3 cross one another. Thus, the notches 8 of thecap 3 are closed by means of the filter sheet 12 so as to preventintrusion of dust through the notches 8.

Subsequently, the piston 4 is inserted into the cylinder 2 from the openend thereof, and finally the cap 3 is fitted upon the open end of thecylinder 2 by moving it along the flat elongate portion 24 of the rod 5.At this time, the projections 9 upon the outer periphery of the cylinder2 adjacent to the open end thereof are engaged within the grooves 11formed within the inner periphery of the cap 3. Since the projections 9each have the inclined surface 9' and the grooves 11 are tapered, bystrongly coupling the two components together, either one or both of thecap 3 and cylinder 2 are slightly curved or flexed. When the projections9 proceeding along the grooves 11 reach the engagement holes 10, theyare engaged within the engagement holes 10 by means of the elasticrestoring force of either one or both of the cap 3 and cylinder 2. Thecap is thus retained against withdrawal from cylinder 2 (FIGS. 13 and15).

The flat elongate portion 24 of the rod 5 is passed through the cap 3and then turned through means of 90 degrees within the circular hole 7(FIG. 14).

The operation of the air damper 1 thus assembled will now be described.During the elongation stroke of the rod 5, negative pressure is producedwithin the front compartment 2a of the cylinder 2 and upon the left sideof the piston 4. Thus, the contact portion 20 of the valve 18 is broughtinto close contact with the exhaust holes 19 so as to close all theexhaust holes 19. At this time, the contact portion 20 is also broughtinto contact with the orifice 17. However, since the vent groove 23 isopen beyond the outer periphery of the contact portion 20, the twocompartments 2a and 2b are in communication with each other by means ofthe orifice 17 and vent groove 23 (FIG. 16(a)). For this reason, airwithin the rear compartment 2b of cylinder 2 and located upon the rightside of the piston 4 flows through the orifice 17 and vent groove 23into the front compartment 2a upon the opposite side of piston 4 and, atthis time, it is throttled by means of the orifice 17 and vent groove23. Thus, braking force is produced during the elongation stroke of therod 5.

The braking force at this time is determined by means of the gap ldefined between the bottom of the vent groove 23 and the contact portion20 of the valve 18, the gap varying with the speed of the piston 4. Morespecifically, during the movement of the piston 4 the pressure of airwithin the rear compartment 2b of the cylinder 2 causes deformation ofthe contact portion 20 of the valve 18 such that portion 20 partlyenters the vent groove 23 so as to reduce the gap l noted above (FIG.16(b)). Thus, while the load impressed upon the air damper 1 is low, thespeed of the piston 4 is comparatively low, and consequently the extentof deformation of the valve 18 is slight. Therefore, the valve 18 entersthe vent groove 23 to a slight extent. Thus, the gap noted above islarge, and the braking force is comparatively small. When the load islarge, on the other hand, the piston 4 tends to be moved quickly, thusincreasing the pressure exerted upon the contact portion 20 of the valve18 and the extent of the deformation of the valve 18. Thus, the valve 18deeply intrudes into the vent groove 23 so as to reduce the gap l andincrease the force. This means that the braking force is increased witha corresponding increase of the load. It is thus possible to maintain asubstantially constant speed of the piston 4 irrespective of themagnitude of the load.

As shown above, the amount of air flowing into the orifice 17 isdetermined by means of the gap defined between the valve 18 and the ventgroove 23. It is thus possible to provide the orifice 17 with acomparatively large diameter.

Thus, it is possible to form the orifice 17 using a core pin (not shown)during the plastic molding operation. In the illustrated embodiment thediameter of the orifice is predetermined to be 1 mm. However, it ispossible to obtain the same orifice effect in the case of an orificediameter of 0.2 mm or less as a result of the definition of the gapbetween the valve 18 and the bottom of the vent groove 23.

However, it is very difficult to form the orifice 17 with a diameter of0.2 mm or less from the outset by using a core pin. This is so becausewhen a very thin core pin is used, it is liable to be bent or brokenduring the molding operation. For this reason, the lower limit of theorifice diameter is 0.3 mm in the case where a core pin is used.According to the invention, the orifice 17 has a diameter of 1 mm, sothat it can be readily formed by using a core pin. Furthermore, the ventgroove 23 can be more readily formed than a hole, and is therefore moreamenable to high precision machining.

It is possible to form holes after formation of the orifice 17. In thiscase, an increased number of steps are involved as compared to the caseof simultaneous molding, and hence the manufacturing process iscorresponding complicated. In the case of using a drill (not shown) forachieving hole formation, it is difficult to ensure a constant diameterof a very small hole such as, for example, the orifice 17, and thus therejection factor is high. In the case of using a press, the lower limitof the hole diameter is 0.25 mm. In addition, only shallow holes can beformed. In this case, therefore, the orifice effect is low.

The braking force is variable depending upon the position of the piston4. More specifically, during the initial stage of the stroke, the O-ring15 is engaged and elastically deformed by means of the ribs 6 providedupon the inner periphery of the cylinder 2, thus producing a gap betweenthe inner periphery of the cylinder 2 and the outer periphery of O-ring15 of the piston 4. For this reason, during the initial stage of thestroke of the piston 4 air flows through the gap noted above and intothe front compartment 2a of the cylinder 2, whereby the braking force iscorresponding reduced. When the piston is moved to a certain extent, onthe other hand, the ribs 6 cease to exist, and the O-ring 15 is restoredto its original undeformed state so as to be in close contact with theinner periphery of the cylinder 2 without any gap formed between thetwo. Thus, only air having passed through the vent groove 23 enters thefront compartment 2a through means of the orifice 17, this increasingthe braking force. During the initial stage of movement of the piston 4,the piston 4 moves smoothly even though the load is comparatively small.

During the contracting stroke of the rod 5, since the front compartment2a of the cylinder 2 is in an increased pressure state, the valve 18opens the orifice 17 and exhaust holes 19, and thus the two compartments2a and 2b are in communication with each other by means of the orifice17 and exhaust holes 19 in their fully open state. Air within the frontcompartment 2a is thus discharged into the opposite side rearcompartment 2b through means of the orifice 17 and exhaust holes 19, andno braking force acts upon the movement of the rod 5 in the contractingdirection.

During the contracting stroke of the rod 5, noise is liable to begenerated by means of the resistance presented to the air flowingthrough the orifice 17 and exhaust holes 19, and the valve 18 resonateswith this noise, thus amplifying it. In order to prevent this noise fromoccurring due to the valve 18, the point of resonance is shifted byimproving the hardness or shape of the valve 18. In addition, in thisembodiment air having passed through the orifice 17 and exhaust holes 19reaches the sound-proof packing 28 after passing through the gapsdefined between adjacent leg portions 26 of the rod 5. Thus, noisegenerated from the orifice 17, exhaust holes 19 and valve 18 isattenuated when the air passes through the packing 28.

In the illustrated embodiment, the piston 4 is molded separately fromthe rod 5. However, it is possible to form both the piston 4 and rod 5as a one-piece molding. Furthermore, while in the embodiment describedabove, the braking force is provided during the elongation stroke of therod 5, it is possible to provide a braking force during the contractionstroke of the rod 5 by increasing the sealing property of the rearcompartment 2b of the cylinder 2 upon the open end side thereof byreversely mounting the valve 18. Furthermore, the number, shape andlength of the ribs 6 of the cylinder 2 are not limited to those shown inthe above illustrated embodiment. For example, by providing ribs 6 suchthat their sectional areas are gradually reduced from the blind end sidetoward the open end side of the cylinder 2, smoother movement of thepiston 4 can be obtained. Furthermore, it is possible to perform brakingforce control depending upon the number and sectional profile of theribs.

Now, an example of use of the air damper 1 having the above constructionwill be described in conjunction with an embodiment illustrated in FIG.17. In the Figure, reference numeral 34 designated a housing open atleast upon the front, and 35 a door for opening and closing the frontopening of the housing 34. The door 35 has its lower end hinged at theopening of the housing 34. Thus, when it is opened, it is pivoteddownwardly about a shaft 36 at the lower end thereof by means of its ownweight. It is locked in its open state by suitable locking means (notshown) capable of being released. The door 35 may be biased in theopening direction by spring means.

The blind end 2' of the cylinder 2 of the air damper 1 is pivoted to asurface of the housing 34, and the rod end 5' is pivoted to a surface ofthe door 35.

In operation, when the door 35, disposed in the closed state is pivoteddownwardly by means of its own weight and is thus opened, the rod iselongated. The air damper 1 thus produces a braking force, and the door35 opens slowly and quietly (to the state as shown by means of thephantom line in FIG. 17).

At this time, as the door 35 pivots downwardly, the load upon the rod 5is progressively increased. For this reason, during the initial stage ofopening of the door 35 the load is small, but during this stage thebraking force is also low due to the ribs 6 provided upon the innerperiphery of the cylinder 2. Thus, the piston 4 is moved comparativelyquickly despite the small load. When the door 35 has opened to a certainextent, the load on the rod 5 increases. However, since the ribs 6 arenot present so as to no longer engage the piston 4 when the latter is atits intermediate stroke position within the cylinder 2, the brakingforce increases so as to correspondingly reduce the speed of the piston4.

In addition, along with load increase the gap l defined between thevalve 18 and the bottom of the vent groove 23 is gradually reduced so asto gradually increase the braking force.

Thus, a substantially constant speed of the piston 4 can be maintainedeven with load increase, and the door 35 opens at a substantiallyconstant speed.

When closing the door 35, on the other hand, the rod 5 is contracted,and hence the air damper 1 provides no braking force, and the door 35can thus be correspondingly closed lightly and quickly.

The air damper 1 may be used not only for a case where the load varies.In this embodiment of the air damper 1, a constant braking force can beobtained except for the initial braking provided that the load isconstant. Therefore, it is possible to use the air damper according tothe invention for a case where a constant braking force is necessary. Ofcourse in such case the ribs 6 may be omitted. Furthermore, for a casewhere the load is reduced during an initial braking stage and isotherwise constant, only ribs 6 may be provided, while providing anorifice 17 within an area other than the area subject to closing bymeans of the valve 18. Furthermore, since the sound-proof packing 28 isprovided, the air damper according to the invention is suitable for acase in which noise must be avoided, or for high grade products. Thesound-proof packing 28 may of course be omitted in a case where noisemay be generated to a certain extent.

As has been described in the foregoing, according to the invention thebraking force is varied in a direction tending to cancel or compensatefor changes in the load, thus permitting a substantially constant speedof the piston to be maintained.

In addition, with the air damper provided with the vent groove betweenthe orifice and the valve, the amount of air flowing through the orificeis determined by means of the gap defined between the valve and the ventgroove, and it is possible to define a comparatively large orificediameter and permit ready manufacture of the air damper.

Furthermore, with the air damper having the cylinder thereof providedwith ribs, the ends of the ribs are in frictional contact with the outerperiphery of the piston, and thus it is possible to improve thesmoothness of the piston movement.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the presentinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A cylinder type air damper, comprising:a cylinder; a piston inserted for reciprocation within said cylinder and axially dividing the interior of said cylinder into a front compartment and a rear compartment; orifice means axially penetrating said piston so as to permit an exchange of air between said two compartments in response to axial movement of said piston within said cylinder; a valve operatively associated with said orifice means for blocking said exchange of air between said two compartments through said orifice means in response to said axial movement of said piston within said cylinder in one direction, said orifice means being disposed within an area subject to said blocking by said valve, and for permitting unobstructed exchange of air between said two compartments when said piston undergoes axial movement within said cylinder in a direction opposite to said one direction; and a vent duct being in communication with said orifice means and extending beyond said valve such that said vent duct communicates at one end thereof with said orifice means and opens at the other end thereof within an area other than said area subject to said blocking by said valve so as to permit a throttled exchange of air between said two compartments when said piston undergoes said axial movement in said one direction.
 2. An air damper as set forth in claim 1, further comprising:a cap lockingly engageable upon an open end of said cylinder, and having an axially located aperture defined within an end wall of said cap for permitting a piston rod of said piston to extend therethrough and outwardly of said cylinder, for substantially closing said open end of said cylinder.
 3. An air damper as set forth in claim 2, wherein:said open end of said cylinder has a plurality of detents mounted upon an external peripheral surface thereof; and said cap has a plurality of apertures defined within a peripheral wall portion thereof for receiving said detents of said cylinder so as to lockingly engage said cap upon said cylinder.
 4. An air damper as set forth in claim 2, further comprising:filter means disposed interiorly of said cap and interposed between said end wall of said cap and said open end of said cylinder.
 5. An air damper as set forth in claim 1, wherein:said orifice means comprises a plurality of apertures disposed upon a circular locus about a longitudinal axis of said piston.
 6. An air damper as set forth in claim 1, wherein:said valve has a substantially T-shaped configuration in cross-section.
 7. An air damper as set forth in claim 1, further comprising:a piston rod separable from said piston; and means for lockingly engaging said piston and said piston rod.
 8. An air damper as set forth in claim 7, wherein said means for lockingly engaging said piston and piston rod comprises:a plurality of detents mounted upon said piston rod at predetermined first circumferential positions, and a plurality of diametrically opposed guide grooves formed within a peripheral wall portion of said piston rod; and a plurality of substantially T-shaped fingers mounted upon said piston for engaging said plurality of detents upon said piston rod, and a plurality of diametrically opposed guides mounted upon said piston for receptive disposition within said guide grooves of said piston rod.
 9. An air damper as set forth in claim 1, wherein:said vent duct has a predetermined depth defined within said piston so as to control the amount of air flowing therethrough when said piston is moved in said one direction.
 10. An air damper as set forth in claim 1, further comprising:means integrally provided upon said cylinder for mounting said cylinder upon an enclosure; and means integrally provided upon said piston rod for mounting said piston rod upon a closure pivotably mounted upon said enclosure such that said air damper can dampingly control movements of said closure relative to said enclosure.
 11. A cylinder type air damper, comprising:a cylinder; a piston inserted for reciprocation within said cylinder and axially dividing the interior of said cylinder into a front compartment and a rear compartment; orifice means axially penetrating said piston so as to permit an exchange of air between said two compartments in response to axial movement of said piston within said cylinder; a valve operatively associated with said orifice means for blocking said exchange of air between said two compartments through said orifice means in response to said axial movement of said piston within said cylinder in one direction as a result of said orifice means being disposed within an area of said piston which is subject to said blocking by said valve, and for permitting unobstructed exchange of air between said two compartments when said piston undergoes axial movement within said cylinder in a direction opposite to said one direction; O-ring means disposed about said piston and in surface contact with an inner peripheral wall surface of said cylinder as said piston reciprocates within said cylinder so as to normally establish a seal between an outer peripheral portion of said piston and said inner peripheral wall surface of said cylinder; and at least one rib provided upon said inner peripheral wall surface of said cylinder so as to project radially inwardly into said interior of said cylinder and toward said outer peripheral portion of said piston, and so as to extend axially within said cylinder for a predetermined axial length of said cylinder so as to encounter said O-ring means of said piston and radially inwardly deform said O-ring means of said piston in order to break said seal normally established by said O-ring means between said outer peripheral portion of said piston and said inner peripheral wall surface of said cylinder so as to permit an exchange of said air between said two compartments.
 12. The air damper according to claim 11, wherein:said at least one rib extends axially from the inner surface of a blind end of said cylinder.
 13. An air damper as set forth in claim 11, wherein:said at least one rib comprises a plurality of ribs disposed parallel to one another.
 14. An air damper as set forth in claim 13, wherein:said plurality of ribs extend axially within said cylinder for said predetermined length which is approximately one-third of the axial length of said cylinder.
 15. An air damper as set forth in claim 11, wherein:said orifice means comprises a plurality of apertures disposed upon a circular locus about a longitudinal axis of said piston.
 16. An air damper as set forth in claim 11, wherein:said valve has a substantially T-shaped configuration in cross-section.
 17. A cylinder type air damper, comprising:a cylinder; a piston inserted for reciprocation within said cylinder and axially dividing the interior of said cylinder into a front compartment and a rear compartment; O-ring means disposed about said piston and in surface contact with an inner peripheral wall surface of said cylinder as said piston reciprocates within said cylinder so as to normally establish a seal between an outer peripheral portion of said piston and said inner peripheral wall surface of said cylinder; orifice means axially penetrating said piston so as to permit an exchange of air between said two compartments in response to axial movement of said piston within said cylinder; at least one rib provided upon said inner peripheral wall surface of said cylinder so as to project radially inwardly into said interior of said cylinder and toward said outer peripheral portion of said piston, and so as to extend axially within said cylinder for a predetermined axial length of said cylinder so as to encounter said O-ring means of said piston and radially inwardly deform said O-ring means of said piston in order to break said seal normally established by said O-ring means between said outer peripheral portion of said piston and said inner peripheral wall surface of said cylinder so as to permit an exchange of said air between said two compartments; a valve operatively associated with said orifice means for blocking said of air between said two compartments in response to said axial movement of said piston within said cylinder in one direction, said orifice means being disposed within an area subject to said blocking by said valve, and for permitting unobstructed exchange of air between said two compartments when said piston undergoes axial movement within said cylinder in a direction opposite to said one direction; and a vent duct being in communication with said orifice means and extending beyond said valve such that said vent duct communicates at one end thereof with said orifice means and opens at the other end thereof within an area other than said area subject to said blocking by said valve so as to permit a throttled exchange of air between said two compartments when said piston undergoes said axial movement in said one direction.
 18. An air damper as set forth in claim 17, wherein:said orifice means comprises a plurality of apertures disposed upon a circular locus about a longitudinal axis of said piston.
 19. An air damper as set forth in claim 17, wherein:said valve has a substantially T-shaped configuration in cross-section.
 20. An air damper as set forth in claim 17, wherein:said vent duct has a predetermined depth defined within said piston so as to control the amount of air flowing therethrough when said piston is moved in said one direction. 